It is proposed that the clones which have already been generated in PBR322 to total immunoprecipitated TAT RNA from Drosophila hydei polytene tissue be in situ hybridized to D. hydei and D. melanogaster polytene chromosomes to determine whether any of these clones contain the TAT gene. The TAT gene is located at band II-48C in D. hydei salivary polytene chromosomes. Poly A TAT mRNA will be isolated, in vitro translated and if the above clones do not contain the TAT gene they will be used for cDNA synthesis and the cDNA used for cloning. The cloned TAT cDNA will be used as probes to isolate the native gene from genomic libraries of D. melanogaster and D. hydei. The role of pyridoxine in the induction of the TAT gene will be examined using the cloned TAT genes as well as with indirect immunofluorescence to the salivary polytene chromosomes using antibodies prepared against pyridoxine and deoxpyridoxine. A series of ebony mutants (located at the II-48 band) will be examined for alteration in TAT activity as well as for alterations in electrophoretic mobility. Finally seeing that the D. hydei TAT antibody cross reacts with rat liver homogenates we will perform a series of preliminary experiments to determine whether the D. hydei TAT clones may be used to isolate the TAT gene from libraries of rat DNA.